1. Field of the Invention
The present invention is directed to methods for preconditioning and/or providing neuroprotection to the animal central nervous system against ischemia, neurodegeneration, trauma and metal poisoning, including associated cognitive, behavioral and physical impairments.
2. Description of the Related Art
Certain medical procedures, for example coronary artery bypass graft (CABG) surgery, are associated with neurological complications. In the case of CABG, the surgery is performed on more than 800,000 patients worldwide each year. Many of the CABG procedures performed are associated with neurological complications. These complications range from stroke in up to 16% of the patients to general cognitive decline with 50% of patients having impairment post-surgery and with progressive decline occurring in some patients over the next five years. In addition, physical and behavioral impairment manifest in some CABG patients. Newman M F et al., N. Eng. J. Med. 344:395-402 (2001); Brillman J., Neurol. Clin. 11:475-495 (1993); and Selnes, O. A., Ann. Thorac. Surg. 67:1669-1676 (1999) are instructive.
Originally, it was hypothesized that the neurological complications associated with CABG surgery were either procedure or patient-related. The procedure generally implicated as potentially harmful was cardiopulmonary bypass using a pump and oxygenator. However, a recent study reports no difference in cognitive outcome between groups of patients undergoing CABG surgery performed with, or without, the pump and oxygenator. Such results suggest that the neurological impairments following CABG surgery may, in fact, be patient-related and, as a result, amenable to therapeutic manipulation.
In addition, patients at risk for, or diagnosed with disorders involving neurological impairments, e.g., Alzheimer's disease, Parkinson's disease, stroke, traumatic brain injury, spinal cord injury may benefit from similar therapeutic manipulation. See Crapper McLachlan, D. R., Dalton, A. J., Kruck, T. P. A., Bell, M. Y., Smith, W. L., Kalow, W., and Andrews, D. F. Intramuscular desferrioxamine in patients with Alzheimer's disease. The Lancet 337:1304-1308, 1991.
A number of neurodegenerative disorders are known to have metal-associated pathology, i.e., resulting at least in part from metal poisoning, and may benefit from the therapeutic manipulation contemplated by embodiments of the present invention. These include AD, PD, Creutzfeldt-Jakob disease, familial amyotrophic lateral sclerosis, lewy-body dementia, carotid atherosclerosis, tardive dyskinesia, multiple sclerosis, Wilson's disease, progressive supranuclear palsy, Hallervorden-Spatz syndrome, multisystem atrophy, Huntington's disease, familial basal ganglia degeneration, Down's syndrome, cataracts, haemochromatosis, cerebral hemorrhage and head injury. See P. M. Doraiswamy and A. E. Finefrock, Metals in our minds: therapeutic implications for neurodegenerative disorders, The Lancet Neurology, Vol. 3, July 2004.
In general, ischemic conditions activate a number of genes that are important in the cellular and tissue adaptation to low oxygen conditions. These genes include erythropoietin, glucose transporters, glycolytic enzymes, and the vascular endothelial growth factor (VEGF). VEGF is a major angiogenic factor that has been shown to activate new blood vessel formation. Transcriptional up-regulation has been shown to be implicated in the induction of the VEGF gene, an action mediated by the specific binding of the hypoxia-inducible factor-1 (HIF-1) to the hypoxic response element (HRE).
The HIF-1 transcription factor is a heterodimer composed of HIF-1α and HIF-1β and regulates the adaptive response to hypoxia in animal cells. HIF-1α accumulates under hypoxic conditions, but is virtually undetectable in normal oxygen conditions. HIF-1β, on the other hand, is readily found in all cells. The HIF-1 heterodimer is believed to be neuroprotective against ischemia through the activation of EPO and VEGF.
HIF-1α has been shown in vitro to be activated by metal chelators, including both iron and copper chelating agents. A particular example of such an agent is deferoxamine (DFO), a hexadentate iron chelator, with kinetics similar to those associated with hypoxia, resulting in increased expression of HIF-1 target genes, including EPO and VEGF. DFO is also known to stabilize HIF-1 subunits, possibly by chelating and inactivating the iron that plays a role in targeting the subunit for proeolytic degradation under normoxic conditions.
In vivo studies have demonstrated that DFO induces HIF-1α in neonatal and adult rats, injecting the chelator either subcutaneously (s.c.) or intraperitoneally (i.p.), typically in very high dosage. In addition, studies indicate that the following substances stimulate and/or stabilize HIF-1α: insulin, IGF-I, heregulin insulin, heregulin, TGFbeta, IL-1 beta, TNFalpha, cobalt, pyruvate, oxalacetate and lactate.
Problems exist, however, with the administration of DFO intravenously. DFO is not generally injected intravenously for at least two reasons. First, it is a small molecule and, as a result, is eliminated rapidly through the kidney. The typical plasma half-life in humans is less than 10 minutes. Second, the injection of an intravenous bolus of DFO causes acute hypotension that is rapid, may lead to shock and may be lethal. These characteristics have limited the utility of DFO in particular as a neuroprotective agent.
One published study administered DFO intranasally to iron overloaded patients. G. S. Gordon et al., Intranasal Administration of Deferoxamine to Iron Overloaded Patients, (1989) Am. J. Med. Sci. 297(5):280-284. In this particular study, DFO was administered to the patients as a nasal spray in a volume of 75 microliters per spray. Significantly, such sprays are known to deposit the drug or other substance in the lower third of the nasal cavity. This is verified by patient observations stating that a bad taste in the mouth was resulting from the drug passing through the nasopharynx and into the mouth. As a result, this study did not involve delivering the drug to the upper third of the nasal cavity. Thus, the drug would not have reached the olfactory epithelium or the olfactory nerves. As a result, delivery of the drug to the CNS would be less than optimal.
It is recognized that intranasal delivery to the CNS may occur along both the olfactory and trigeminal nerve pathways. See Thorne, R G (2004), Delivery of Insulin-Like Growth Factor-I to the Rat Brain and Spinal Cord Along Olfactory and Trigeminal Pathways Following Intranasal Administration, Neuroscience, Vol. 127, pp. 481-496. Optimal delivery taking advantage of both pathways is accomplished by administering the substance in the upper third of the nasal cavity.
Regarding Alzheimer's disease, some studies indicate that cerebral vascular problems occur first, followed by neurodegeneration in later stages of the disease. For example, see The Lancet Neurology, vol. 3, page 184-190, Jack C. de la Torre (March, 2004). Thus, it may be possible to prevent, mitigate or treat the effects of Alzheimer's disease at the appropriate disease stage through therapeutic manipulation targeted toward mitigation or prevention of cerebral ischemia or neurodegeneration.
In a published patent application, U.S. Pat. App. No. 20020028786 by William H. Frey II (also a co-inventor of the present application) entitled METHODS AND COMPOSITIONS FOR ENHANCING CELLULAR FUNCTION THROUGH PROTECTION OF TISSUE COMPONENTS, various substances are discussed that may be administered intranasally to treat various diseases and conditions. The entire contents of this reference are hereby incorporated by reference.